1. Field of the Invention
The present invention generally relates to a method for bending a work piece that is used to convey a liquid, a gas or a solid, including a powder, or a combination thereof, and a device for bending the pipe. More particularly, the present invention relates to an exhaust pipe connecting together an engine and a muffler of a motorcycle, a snowmobile, a four wheeled buggy, and the like.
2. Description of the Related Art
Conventionally, a curved section of a conveyance pipe can be formed with a stainless steel pipe that has been bent to be a certain configuration. This kind of pipe preferably has a fixed inner diameter so that a fluid can flow smoothly through its inner cavity, or, in the case of an exhaust pipe, a pressure wave is not unnecessarily reflected midway. However, when a pipe is bent, the inside surface of the pipe is uneven because the outer radius of curvature is larger than the inner radius of curvature. The conventional pipe thus has a drawback that a curved portion thereof can be partially flat at a bent portion, which naarows the inner cross sectional area.
Such a drawback can be corrected to a certain extent if the pipe is bent while a liquid is enclosed within the inner cavity of the bent portion and the pipe is tightly closed (for example, JP-A-2002-254112 (Pages 1 through 12 and FIGS. 1 through 14)).
However, in this bending device, for bending a plurality of portions of a single work piece, when a setup change is made from one bending process to a subsequent bending process, a three way valve is switched so that water can be returned to a water tank from a high pressure pump, and a water pressure in the work piece is decreased to zero during every setup change. Thus, the number of steps involved increases which ultimately decreases efficiency.
Also, in the bending device, a bent work piece is wound around a roll mold. Processes are provided for removing the completed work piece from the roll mold and temporarily placing the completed work piece to one side while the next work piece is carried to the roll mold. Processes also are provided for carrying the bent work piece or a subsequent work piece, which will have been temporarily placed to one side. In addition, processes are provided for removing the completed work piece from the roll mold and carrying the completed work piece away and then subsequently placing a temporarily placed work piece on the bending device for completion.
Therefore, problems are caused. For example, a long time is necessary to remove the bending-finished work piece that is wound around the roll mold and to mountthe bending-finished work piece that is going to be bent next. Also, space must be provided in which a work piece can be temporarily set aside. Thus, the size of the device must be increased.
An object of a first invention is to provide a method for bending a work piece and a device for bending the work piece both of which can reduce the number of steps involved and can improve the working efficiency.
Also, an object of second and third inventions is to provide a method for bending a work piece and a device for bending the work piece both of which can save time for removing a bending-finished work piece and for setting another material that is going to be bent to improve the productivity, and can contribute to making the device compact.